I would like to use tcpflow to monitor https requests. I have read tutorials on how to monitor http traffic but when I connect to a host using https the output is garbled. I am using tcpflow in the following manner:

You're missing the point of HTTPS. You cannot read (much) meaningful information from a HTTPS stream, as the TCP layer encapsulating it is encrypted. Ultimately that means that the data will look like garbage to anyone trying to intercept it (including you).